UPS drivers put a lot of miles on their vehicles, and they burn a lot of fuel. A few years ago, the company hit on a wacky idea to conserve fuel and reduce costs: don’t turn left.

You might remember seeing Mythbusters tackle this one as a mini-myth (that’s where the header image above came from). In just two TV minutes, Grant, Tory, and Kari confirmed that while routes with left turns were faster, they also burned substantially more fuel.

UPS kicked off their boycott of left-hand turns back in 2004. As of 2012, they had already saved an impressive 10 million gallons of fuel by switching to right-turn-heavy routes. The company also figures that carbon emissions were reduced by around 100,000 metric tons. That’s roughly equivalent to taking 5,300 passenger vehicles off the road for an entire year.

Right turns also reduced damages to UPS delivery vehicles, though UPS doesn’t provide any specific numbers. Drivers attempting to turn across traffic are among those most frequently involved in accidents, so avoiding left turns helps keep UPS drivers out of harm’s way. It’s not just damages that would cost UPS money — downtime hurts, too.

The algorithms that UPS uses to map out routes is much more refined now than it was in the early days. And yes, sometimes UPS drivers do turn left. It usually only happens in residential neighborhoods where there’s very little traffic.

It happens less than once every ten turns, but even then it’s probably under protest. UPS drivers that have been interviewed before have made it very clear: they hate making left turns. Fortunately, UPS’ software engineers are all too happy to help keep them to minimal levels.